This Mentored Research Scientist Development Award will provide the applicant, a doctorally and postdoctorally educated physical therapist, with the training necessary to achieve the long-term objective of an independent career in rehabilitation research. The applicant's expertise in the study of neural control of locomotion will be combined with the sponsor's expertise in the evaluation, treatment, and study of individuals with Parkinson's disease. The training provided will allow the applicant to investigate mechanisms underlying gait difficulties in individuals with Parkinson's disease, with the ultimate goal of developing rehabilitative strategies to maximize functional mobility in these individuals. The proposed studies will focus on turning during walking, as many subjects with Parkinson's disease have difficulty with turning and little research has focused on this functionally critical movement. The proposed studies will address the following hypotheses: 1) problems with the selection and production of appropriate motor patterns contribute to impaired turning movements, 2) conventional pharmacological treatments partially improve turning motor patterns but do not completely address the problem, 3) subjects with Parkinson's disease retain the ability to modify locomotor output and produce appropriate turning patterns when provided with relevant external stimuli, and 4) rotating treadmill stimulation may be an effective rehabilitative tool for providing these external stimuli, thereby enhancing turning ability. All of these hypotheses will be investigated using whole-body, 3-D movement analyses in conjunction with electromyographic recordings. Subjects with Parkinson's disease will be compared to age- and gender-matched control subjects. Results of the proposed studies will provide important insights regarding the effects of Parkinson's disease on gait, evaluate the effectiveness of current therapies in addressing gait difficulties, and guide future rehabilitation strategies for improving functional mobility in people with Parkinson's disease.